Abstract:

Electroless nickel plating is a part of electroless nickel immersion gold (ENIG)-surface finish used in printed circuit board (PCB) manufacturing. In the ENIG-surface finish, the electroless nickel alloy prevents the oxidation of a circuitry by working as a diffusion barrier between the coppered circuitry and protective gold alloy and protecting the circuitry from mechanical tearing.

It is well-known that the thickness and phosphorous content of the electroless nickel alloy have a dramatic effect on the PCB's characteristics. Unfortunately, these parameters cannot be directly measured during the plating process which makes it impossible to control the parameters in traditional way.

In this thesis a new model for electroless nickel plating process is developed using electrochemical reaction mechanism and mixed potential theory. The model inputs are the standard online measurements of PCB plating line. From these the model produces accurate realtime estimates inter alia from alloy thickness, phosphorous content, by-product concentrations and current densities of partial reactions. The developed model has been tested against independent data gathered from three active and several passive experiments conducted in an industrial PCB manufacturing line. In all the experiments, the model shows good agreement with the data and correct response to the changes in plating conditions. The behavior of the model is in a good agreement with the literature and former research results.

It the thesis, the model is applied in model-based monitoring of an industrial plating process and it is shown to be capable of estimating online the unobservable product and electrical process parameters from standard measurements of PCB-industry.

Based on the model also a new sophisticated control algorithm is developed. The algorithm calculates the optimal nickel ion concentration and pH trajectories by which the desired alloy thickness and phosphorous content are reached. These trajectories are tracked by PI-controlled pumping of ammonia and nickel sulphate. The performance of the control algorithm is tested by simulation and it is shown to be effective.Autokatalyyttinen nikkelipinnoitus on osa piirilevyjen valmistuksessa käytettävää nikkeli-kulta -pintaviimeistelyä. Tässä prosessissa autokatalyytinen nikkeli suojaa virtapiiriä hapettumiselta estämällä diffuusion kuparisen virtapiirin ja suojaavan kultaisen pintakerroksen välissä. Samalla nikkelikerros parantaa virtapiirin kulutuskestävyyttä.